1. Field of the Invention
The present invention relates to a method of manufacturing a laminated core for a dynamo-electric machine and particularly to a method of manufacturing a laminated core for a dynamo-electric machine, in which a core of a dynamo-electric machine such as a small-sized DC motor, a generator, etc. is a plurality of core sheets formed in a stack, and to a laminated core manufactured by use of the same method.
2. Description of the Related Art
Generally, a laminated core has been used in dynamo-electric machines such as a small-sized DC motor, a generator or the like.
In order to form such a laminated core, a plurality of thin core sheets 12 having a circular through hole 10 formed in the center thereof are provided by a die-cutting operation, as indicated in FIG. 4. Next, the plurality of core sheets 12 are disposed in a stacked state in a magazine on a cut-out slider 14 in a position A shown in the same drawing. Thereafter, a predetermined number of core sheets 12 provided in the magazine are placed in a position B. The shaft 16 is then forced into the through holes 10 of the core sheets 12. The predetermined number of core sheets 12 are then laminated together in a stack so as to be disposed in alignment with the shaft 16, thereby allowing a laminated core 18 to be formed.
However, in the case of the above-mentioned method of manufacturing a laminated core, thin plates are first punched by means of a press die and aligned with one another to be conveyed. The shaft 16 must then be forced through the core sheets using rotating and skewing operations for balance purposes. This process, however, requires many steps and much labor making it troublesome. Automating such production is difficult. When an automated process for producing a laminated core is used, it is expensive.
Accordingly, in order to solve the problems in the above-described processes, lamination methods as shown in FIGS. 5 and 6 have been conventionally employed.
FIG. 5A is a plan view of a core sheet. FIG. 5B is a vertical sectional view of FIG. 5A, and FIG. 5C is a vertical sectional view after a shaft has been forced through the core sheets.
In a center portion of a core sheet 20 a through hole 24 is provided for inserting a shaft 22 therethrough. A plurality of slot holes 26 are formed around the periphery of the core sheet 20. On the end of the peripheral portions formed by the slot holes 26, a plurality of protrusions 28 for laminating is formed by press-molding during the die-cutting of the core sheets 20. At the same time the protrusions 28 of each core sheet 20 are fitted with one another so as to laminate the plurality of core sheets 20 together. Thereafter, the shaft 22 is forced through the through holes 24 of the laminated core sheets 20, thereby enabling a laminated core to be formed.
FIGS. 6A, 6B and 6C each correspond to FIGS. 5A, 5B and 5C, respectively. Like elements are given like reference numerals, and hence only the feature portions of FIG. 6 will be explained.
A core sheet 20 is provided with a ring-shaped convex portion 30 formed along the entire inner periphery of a through hole 24 disposed in the center of the core sheet 20. The convex portion 30 is formed by press-molding during punching the core sheet 20 in a manner similar to that in FIG. 5 and is for lamination. At the same time the convex portions 30 of each core sheet 20 are fitted to each other, thereby allowing the plurality of core sheets 20 to be laminated together.
In the above-described conventional methods of manufacturing a laminated core for a dynamo-electric machine, constructions have been provided in which a plurality of protrusions 28 is formed on the end edge of the peripheral portion of a core sheet 20, or a convex portion 30 is formed at the inner periphery of a through hole of the core sheet 20. The protrusions 28 and convex portions 30 are formed by press-molding during die cutting of the core sheet 20, so as to be fitted together with each other. After the core sheets are laminated together, a shaft 22 is forced therethrough. Accordingly, even after the formation of the rotor is completed, the core sheets 20 are connected to each other by the protrusions 28 or the convex portions 30. As a result, a higher degree of adhesion between the core sheets 20 is obtained.
This makes the resistance between the core sheets 12 low, thereby resulting in the generation of iron loss due to an eddy current. Thus, there is a problem in that rotation efficiency, which is an important characteristic of a dynamo-electric machine, will be lowered as compared with that of FIG. 4, in which core sheets 12 are simply laminated to each other.
Also, this conventional method has another problem in that, since space is necessary for forming a protrusion 28 or a convex portion 30 on a part of the core sheet 20, this puts restrictions on the core product configuration with respect to product design.